Means for changing the intensity of signals in radiodynamic receiving systems



E. L. CHAFFEE.

MEANS FOR CHANGING THE INTENSITY 0F SIGNALS IN RADIODYNAIIIIG RECEIVING SYSIEIS. APPLICATION FILED JULY 31.:911. mzucwzo APR. 21, 1921.

1,399,251, Patented Dec. 6, 1921.

I2 k If L l X 2 I I! u 3 1' E E VO LTC VO L76 Inventor.- E'Snorg Leon Wee v' lw UNITED STATES PATENT OFFICE.

EMORY LEON CHAFFEE, OF BELMONT, MASSACHUSETTS.

MEANS FOR GHANGIN G THE INTENSITY OF SIGNALS IN RADIODYNAMIC RECEIVING SYSTEMS.

Application filed July 31, 1917, Serial No. 183,690. Renewed April 21, 1921.

To all. whom it may concern:

Be it known that I, EMORY LEON CHAF- FEE, a citizen of the United States, and a resident of Belmont, in the county of Middlesex and State of Massachusetts, have invented an Improvement in Means for Changing the Intensity of Signals in Radiodynamic Receiving Systems, of which the following description, in connection with the accompanying drawings, is a specification, like characters on the drawings representing like parts.

This invention relates to means for and methods of reducing the intensity of strong signals produced through or, pertaining to radiant energy without reducing the intensit of weak signals, and in its preferred embo iment constitutes an improvement upon the inventions disclosed in the application of John Hays Hammond, J r., and myself Serial No. 177,202, filed June 27, 1917.

In order that the principle ofthe invention may be readily understood, I will disclose a single form or embodiment thereof and the best mode known to me for practising the invention.

In the drawing? Figure 1 represents diagrammatically the t pe of curve essential to the 'proper operation of the invention;

Fig. 2 represents a family of curves illustrating the advantage of a high difference of potential between the grid and the filament; and

Fig. 3 is a diagram disclosing in detail a receiving system constructed in accordance with the preferred embodiment of the invention.

Fig. 4 is a diagram of a modified portion of the receiving system shown in Fig. 3.

An important object of the invention is to provide for the reduction of the intensity of strong signals in radio-dynamic work without reducin the intensity of weak signals therein. Hy the accomplishment of such purpose, the interference, in the reception of weak signals, due to nearby powerful transmitting stations or to atmospheric disturbances, known as static, can be greatly reduced.

As set forth in the said application of Hammond and Ghafl'ee, means are provided furnishing a leak generally analogous to a resistance, but which is much more effective for stronger signals than for weak ones.

Specification of Letters Patent.

ticul'ar form of Patented Dec. 6, 1921.

Serial No. 463,360.

Such means, which preferably has a resistance decreasing as the potential increases, is efi'ective, wherever it be placed in the receiving system to cut down the large peaks of potential without efl'ecting the small variations of potential caused by weak signals. In Fig. 1, as also disclosed in said application, I have represented at 1 the type of curve essential'or important to the successful operation of the invention, wherein the ordinates represent current caused to flow through the device when voltages represented by the abscissae are impressed across the terminals of the device. A device havmg such a curve is characterized by the fact that small differences of potential cause ve small currents to flow, while large differences of potential cause disproportionately large currents to flow. The means preferably employed in the practice of my invention, and which generically is shown in said application, may be connected across any part of the receiving system pertaining to the use of radiant energy, and particularly of a receiving system, the voltage whereof is caused to increase by incoming signals or by static disturbances. In such case, the part across which such means is connected Wlll be more or less discharged, such means forming a bypass which is more active for intense signals or disturbances than for weak ones.

The means employed, one form only of which is herein disclosed, may be connected in various ways across the receiving system, and the invention is not limited to that parmeans herein disclosed or to any one of the various ways for'connecting the said means in receiving systems.

In Fig. 3, the primary of an oscillating transformer of an open receiving aerial circuit is represented at 2. The secondary winding of the closed oscillatory circuit is represented at 3 and a tuning condenser at 4. The stoppage condenser is represented at 5, and the audion is represented 'at 6, it being connected through the stoppage condenser to the oscillatory secondary circuit which in turn is coupled to the inductance of the receiving antenna 7. The grid oi said audion is represented at 8, the plate at 9, and the filament at 10. It -is desirable at times to inter-pose in the conductor leading from the grid 8 of the audion 6 means for producing on the grid a small polarizing potential either positive or negative, as may be desired. The purpose of this is to shi the characteristic curve so that it starts at zero current when zero potential *is imgrzssed across the sto age condenser 5.

e form of means for t 1s-purp0se may 1n-- clude a battery 10' having its opposite poles connected tothe grid 8 and to the filament 10 respectively, as shown in Fig. 4. Myinvention, however, is not limited to the use of such potential. The heating battery for said filament is indicated at 11, it being connected with said filament by the conductors 12, '13. The usual battery for the grid 9 is indicated at 14, thetelephones at 15 and the circuit wherein said batte and telephones are included is indicate at 16.

The by-pass generically disclosed 1n said application comprises in part an electron tube 17 which ma be of the eneral form of that of the well known an ion detector, but which functions wholly difierently therefrom. The said tube 17 consists of a highly evacuated member into which is sealed a plate 18, an electron emitting filament 19 and a grid 20 situated between the plate and filament. I am not limited to the construction of electron tube shown, and may employ a filament and plate without the grid. y the use of the id, better results are secured.

If the ament 19 be heated in suitable manner, as by a battery 21, so thatelectrons are emitted by the filament and arelatively large diflerence of potential, as for example fifty volts, be impressed between the grid 20 and the filament 19, thereby making the grid 20 positive,

asses from the filament 19 to said grid 20. ihe grid 20 is connected to the circuit 22 containing said battery 21, by a circuit 23 containing the stronger battery 24 which serves to impress an initial polarizing potential upon the grid 20.

If now the plate 18 be connected to the negative end of the filament 19, practicall no current will pass in the plate circuit. I however, the plate 18 be made slightly positive in potential with respect to the negative end of the filament 19, a current will pass in the plate circuit, the magnitude depending upon the potential as represented by the curve 1 in Fig. 1.- A difference of potential between the plate 18- and the filament 19 of only a volt or so will cause several milliamperes to flow in the late circuit. The advantage of ahigh di erence of potential be tween the grid and the filament 1s illustrated by the family of curves 25 in Fi .2, in which each curve represents the con itions for a certain constant voltage impressed between the grid and the filament. The figures indicating the number of volts upon the curves in Fig. 2 give a rough idea merely of the ma ltudesinvolved.

t is very desirable in practice to keep the a large flux of electrons capacity of the grid of the receiving audion as small as possible with respect to other parts of the apparatus. It would appear that by connecting to the grid 80f thereceiving audion 6, the battery 21 and the battery 24 with other usual apparatus, such as switches and'rheostats, disadvantages would accrue, because such added capacit would prevent the potential of the grid 0 the receiving audion from rising as high as without such added capacity, thereby obviously reducing the intensity of the signal. An important object of m invention is the elimination of this disa vantage, which is preferably effected in the following manner.

All the apparatus, which is necessarily connected to the grid 8 of the receiving audion 6, such as the batteries 21, 24 and other associated parts, I inclose in a metal shield, which may be of an suitable con struction and may for examp e be a box covered with tin foil. I have at 26, 27 represented elements or parts of such box about the battery 24 and have diagrammatically indicated the tin foil at 28. Similarly I have indicated at 29, 30 parts or elements of the box about the battery 21 and have diagrammatically indicated the tin foil surrounding the same at 31. It is not essential that all the parts be inclosed in the same box. The

said batteries 21; 24 and otherauxiliary apparatus form in effect the inside coating of a condenser, the outside coating whereof is the described metallic covering, herein represented as made up of the parts 26, 27 28, 29, 30 and 31. The said metallic coverings are all herein shown as connected together, as by means of the conduct0r32, and are also connected to the junction point of the induction coil 3 and condensers 4, 5 in suitable manner, as by the conductor 33.

Such so-called condenser or pseudo condenser, as it may be termed, is connected in parallel with the. stoppage condenser 5, and is therefore a part of such stoppage condenser. It is therefore necessary only toireduce slightly the size of the stoppage condenser to restore the receiving system to its normal sensitiveness.

The capacity of the extra condenser formed by the batteries and metal coverings may easily be made very small if the clearance between the batteries and the metal covering is slight. Thus the system does not suffer from havin too large a stoppage condenser. In practlce, I have found that a distance of an inch between batteries and covering pertaining thereto gives excellent results. a 1

While I have indicated the by-pass as including a. detector having the general form of an audion detector, it 1s to be understood that I am not limited thereto. Other devices may be employed having the essential characteristics shown by the curve of Fig. 1,

such, for example, as crystal contacts and very fine wires which have a positive temperature coeflicient of' resistance.

The inclosure, shield or covering herein disclosed does not necessarily reduce the. ca-

pacity of the grid 8, but does reduce its capacity with respect to other parts of the apparatus. The addition of unprotected batteries would cause the grid 8 in the disclosed, embodiment of the invention to have capacity with respect possibly to twelve or more other parts of-the apparatus, and this would in effect be the same as connecting acondenser from the rid 8 to such twelve or more other parts. bviously this would be disadvantageous. By inclosing the batteries and connecting the parts as herein disclosed, the grid 8 has capacity only with respect to the unction between the secondary winding 3 and condensers 4 and5, which amounts in effect to connecting a condenser in parallel to the condenser 5, from which no .disadvantage results.

Having thus described one illustrative embodiment of my. invention and the best method known to me for practising the same, I desire it to be understood that although specific terms are employed, they are used in a generic and descriptive sense and not for purposes of limitation, the scope of the invention being set forth in the followin claims.

laims:

1. Means for effecting a reduction of the' 5 intensity of strong signals produced through radiant energy without substantial reduction of the intensity of weak signals said means.

including a highly evacuated electron tube inclosing a plate, grid and filament, abattery for said filament, a battery for said grid, and a metal shield for said batteries electrically connected to said plate to form with said batteries a condenser.

2. Means for eflectin a reduction of the intensity of strong signa s produced through radiant ener without substantial reduction of the intensity of weak signals, said means including a highly evacuated electron tube inclosing a plate, grid and filament, a battery for said filament, a battery for said grid, and an inclosure for said batteries having a covering of tin foil electrically connected to said plate to form with said batteries a condenser.

3.. Areceiving system for radio-dynamic energy having means for reducing the intensity of strong signals without reducing the intensity of weak signals, said means including an oscillatory receiving circuit having a stoppage condenser, a by-pa associated with said oscillatory receiving circuit and having a sealed tube inclosing a filament, plate and grid, batteries for said filament and grid, means cooperating with said bat- 65 teries to form a secondary condenser, and

means connecting said secondary condenser in parallel with said stop age condenser.

4. A receiving system ibr electrical oscillations including an oscillatory element responsive to electrical oscillations, and means for reducing the effect of intense electrical impulses upon said element without reducing the efi'ect of weak electrical impulses upon said element, said means comprising a by-pass' extending around said element and including means forming a condenser connected in parallel with said oscillatory element.

5. A receiving system for electribal oscillationsincluding a condenser responsive to electrical oscillations, and means for 'reducing the effect of intense electrical impulses 41 on said condenser without reducing the e ect of weak electrical impulses upon said condenser, said means comprising a by-pass extending around said condenser, and includingmeans forming a second condenser connected in parallel with said first-mentioned condenser.

6. In a radio receiving system, the combination with an oscillation detector, of an os cillatory element arranged to control said detector, and means for reducing the efi'ect upon said detector of high potential impulses without substantiall reducing the effect of low potential impu ses, said means comprising a by-pass around said oscillatory. element, 'a battery for supplying energy to said by-pass, and means cooperating with said battery and formi therewith a condenser connected in pariifiel with said oscillatory element.

7 In a radio receiving system, the combination with an oscillation detector, of a condenser arranged to control said detector, and means for reducing the efi'ect upon said detector of high potential im ulses without substantially reducin the e ect of low potential impulses, sai means comprising a by-pass around said condenser, a, battery for supplying energfi to said by-pass, and means cooperating wit said battery and formi therewith a condenser connected in paralle with said first-mentioned condenser.

8. In a receivingsystem for electrical impulses, the combination with an oscillatory element, of means for limiting the amplitude of oscillation of said element, including a thermionic valve connected across said element, said valve including a container, and a terminal, ionizing means, and potential gradient changing means arranged in said container, a battery arranged to heat said ionizing means, and 'means cooperating withsaid battery and forming therewith a condenser connected in parallel with said oscillatory element.

9. In a receiving system for electrical im' pulses, the combination with an oscillatory element, of means for limiting the amplitude 180 of oscillation of said element, including a thermionic valve connected across said element, said valve including a container, and a terminal, ionizing means, and potential gradient changing means arranged in said container, a batter arranged to heat said ionizing means, a attery arranged to impress an initial potential upon said potential gradient changing means and means cooperating with said batteries and forming therewith a condenser connected in parallel with said oscillatory element.

, 10. In a receiving system for electrical impulses, the combination with a condenser, of means for limiting the amplitude of oscillation of said condenser, including a thermionic-valve connected across said condenser, said valve including a container, and a terminal, ionizing means, and otential gradient changing means arrange in said container, a battery arranged to heat said ionizing means, and means cooperating with valve including a said battery and forming therewith a condenser connected .in parallel with said first mentioned condenser.

11. an a receiving system for electrical impulses, the combination with a condenser, of means tion of said condenser, including a thermionic valve connected across said condenser, said container, and a terminal, and potential gradient changing means arranged in said container a battery arranged to heat said ionizing means, a battery arranged to impress an initial potential upon said potential gradient changing means and means cooperating with said batteries and forming therewith a condenser connected in parallel with said first mentioned condenser.

In testimony whereof, I have signed my name to, this specification.

EMORY LEON CHAFFEE.

ionizing means,

for limiting the amplitude of oscilla- 

